1. Field of the Invention
The present invention relates to an electric steering device for a watercraft in which a steering operation is performed with power from an electric driving device, and more particularly to an electric steering device for a watercraft in which the electric driving device consumes no electric power while a steering angle is retained, and a control method of the electric steering device.
2. Description of the Related Art
There are cases when a boat, a watercraft having an outboard motor, or the like retains its rudder slightly steered at a certain steering angle to compensate for the influence of a wind direction and/or a tidal current even though it is traveling in a straight direction. Such a steering state is called “counter-steering”. During counter-steering, it is required to continuously apply an appropriate retention force to retain a prescribed steering angle against a steering force by propeller reaction or water current since the rudder receives the steering force by the propeller reaction or the water current pushing the rudder back to a straight traveling state. A similar situation occurs in cases of maintaining turning in traveling, docking, and so forth.
It is required to retain a state in which the driving force of the electric driving device keeps being applied to the rudder to obtain the retention force mentioned above in the electric steering device performing the steering operation by using the electric driving device, such as an electricmotor. However, the electric driving device needs to be constantly supplied with electric power in such a situation. This results in a large consumption of electric power. Furthermore, a steering angle may veer off of a target angle due to propeller reaction and/or a water current in a circumstance that electric power is not sufficiently supplied, such as during a power failure.
To solve such a problem, there is disclosed a steering device which includes a plurality of steering control devices arranged to apply a driving electric current corresponding to the difference between a target steering angle and an actual steering angle to each of a plurality of electric motors thereby steering a steering wheel to a target steering angle, a stoppage detecting device arranged to detect stoppage of a steering operation of the steering wheel, and an electric current reducing device arranged to stop the steering control by a portion of the steering control devices among the plurality of steering control devices when the stoppage detecting device detects that the steering operation of the steering wheel is stopped and reduces the driving electric current applied to the electric motors by the portion of the steering control device when the steering operation of the steering wheel is stopped (see Patent JP-A-2006-076413, for example).
However, there is a problem that a plurality of electric motors and a detecting device are required in the above conventional steering device, thus a construction of the steering device is complicated, which increases the production cost.